Method and apparatus for producing electrostatic charge patterns

Abstract

A method of recording an electrostatic charge pattern representing information to be recorded and generated in the interior of an air-tight envelope or chamber comprising a target towards which charged particles are projected, characterized in that the electrostatic charge pattern is produced within the envelope on an electrically insulating surface of a charge receiving material and (1) according to a first mode the charge pattern from such surface is transferred through an array of closely spaced solid conductors, held a solid electrically insulating matrix, to an uncharged electrically insulating surface of an other charge receiving material removably positioned at the outer side of the envelope or (2) according to a second mode the charge pattern from such surface is transferred through said conductors to an oppositely charged electrically insulating surface of a charge receiving material removably positioned at the outer side of the envelope forming according to the second mode a charge pattern in accordance with the un-neutralized area of the exterior insulating surface.

I claim: 
     
       1. A method of recording information as a pattern of electrostatic charges carried by an insulating charge receiving medium which comprises: a. exposing to a pattern of X-ray, γ-rays, or the like an imaging chamber enclosing a pair of spaced imaging electrodes and containing an ionizable gas having an atomic number of at least 36, which chamber is adapted to produce upon such exposure electrostatic charges therein in a corresponding pattern, while maintaining said gas during said exposure under superatmospheric pressure;   b. arranging interior dielectric charge receiving material within said chamber in a charge receiving position in the space between said electrodes;   c. applying a DC potential across said electrodes to bias said charge pattern onto a surface of said dielectric material;   d. displacing the charge-carrying dielectric material from said charge-receiving position to a charge-transferring position within said chamber, in which transferring position said charge-carrying dielectric surface is disposed in close proximity to the interior ends of an array of discrete closely spaced conductors extending from the interior to the exterior of said chamber; and   e. arranging an exterior dielectric charge-receiving material outside said chamber in close proximity to the exterior ends of said conductor array, whereby said charge pattern is transferred to said exterior dielectric material by way of said conductor array.   
     
     
       2. A method according to claim 1, wherein said gas is xenon. 
     
     
       3. A method according to claim 1, wherein the charge pattern formed on said removable receiving material is developed with an electrostatically attractable material. 
     
     
       4. A method according to claim 1 wherein one of said imaging electrodes is a photocathode and said charged particle pattern is generated by imagewise exposing said photocathode to a pattern of radiant energy representing the information to be recorded. 
     
     
       5. A method according to claim 4, wherein the photocathode is covered with a fluorescent coating that when struck by said rays emit electromagnetic rays having wavelengths for which the photocathode is sensitive. 
     
     
       6. A method according to claim 1 wherein said charge transfer is facilitated by applying a DC potential across a pair of transfer electrodes arranged one within and the other outside the chamber in close proximity to the oppositely facing surfaces of the respective dielectric materials. 
     
     
       7. A method according to claim 6 wherein the polarity of the interior electrode is the same as that of the charges on the dielectric material proximate thereto. 
     
     
       8. A method according to claim 1 wherein said interior dielectric charge-receiving material is moved cyclically between said positions for sequential exposure and including the step of removing residual charges from said material before the same is returned to said charge-receiving position. 
     
     
       9. A method according to claim 8 wherein said dielectric material is photoconductive and said residual charges are removed therefrom by passing said material through a light exposure position to uniformly expose the same to light intermediate said charge-transferring and charge-receiving positions. 
     
     
       10. A radiographic system for operation with a source of X-rays which comprises: a. an imaging chamber enclosing a spaced pair of imaging electrodes;   b. means in said chamber for emitting a pattern of electrostatic charges when exposed to an X-ray image and including an ionizing gas medium;   c. a dielectric material disposed in said chamber in a charge-receiving position adjacent one of said electrodes;   d. means for applying an electrical potential across said electrodes for biasing said pattern of electrostatic charges towards said dielectric material in said charge-receiving position on a surface of said material;   e. an array of discrete closely spaced conductors disposed in the wall of said chambers at a locus spaced from said imaging electrodes, said array having one end of the conductors thereof in said chamber and the other end outside said chamber and extending through the chamber wall;   f. means for displacing said charge-receiving material from said charge-receiving position to a charge-transferring position with the charge-carrying surface thereof in close proximity to the interior ends of said conductors; and   g. means for maintaining an exterior dielectric charge-receiving material in close proximity to the exterior ends of said array, whereby said charge pattern is transferred from the interior to the exterior dielectric material through said array.   
     
     
       11. An imaging system according to claim 10 wherein said imaging electrodes include a photocathode. 
     
     
       12. An imaging system according to claim 10, wherein said gas is xenon gas. 
     
     
       13. An imaging system according to claim 10 including a pair of transfer electrodes, one within and the other without said imaging chamber in close proximity to the surfaces of the respective dielectric material facing away from said array. 
     
     
       14. An imaging system according to claim 10 including means for feeding a web of dielectric material past the exterior ends of said array. 
     
     
       15. An imaging system according to claim 10 wherein said interior dielectric material is an endless web and including means for moving said web cyclically between said positions. 
     
     
       16. An imaging system according to claim 15 wherein said interior dielectric web is photoconductive and including means for exposing said web uniformly to light while moving from said charge-transferring to said charge-receiving position to remove residual charges therefrom prior to recharging. 
     
     
       17. An imaging system according to claim 10 wherein said chamber contains under high vacuum conditions (1) an imaging photocathode, (2) a secondary emission multiplier including a plurality of electron-multiplying narrow passages arranged in substantially parallel relationship to each other and in which electrons emitted by the photocathode can be accelerated in an electric field. 
     
     
       18. An imaging system according to claim 17, wherein the passages have a diameter not larger than 200 microns. 
     
     
       19. An imaging system according to claim 17, wherein the length-to-diameter ratio of the passages is in the range of 100:1 to 50:1. 
     
     
       20. An imaging system according to claim 17, wherein the secondary emission multiplier is a resistive matrix including narrow passages arranged in substantially parallel relationship and whose end openings constitute the input and output faces of the matrix, the two surfaces of said matrix where the passages open out being coated with an electrically conductive layer, the conductive layer on the input face of the matrix serving as an input electrode, a separate conductive layer on the output face of the matrix serving as an output electrode, the distribution and cross-sections of the narrow passages and the resistivity and the secondary-emissive properties of the matrix being such that the resolution and electron multiplication characteristic of any one channel unit area of the device is substantially similar to that of any other channel unit area. 
     
     
       21. An imaging system according to claim 20, wherein the secondary emission multiplier is made of glass tubes that are assembled together in substantial parallel relationship and in which the inner surface of the tube is covered with a substance having secondary electron emissive properties.